Advances in polymerization and catalysts have produced new polymers having improved physical and mechanical properties useful in a wide variety of products and applications. With the development of new catalysts, the choice of polymerization, such as solution, slurry, high pressure, or gas phase, for producing a particular polymer has been greatly expanded. Advances in polymerization technology have also provided more efficient, highly productive and economically enhanced processes.
Metallocene catalysts have been widely used to produce polyolefins such as polyethylene polymers. They have provided efficient processes and a variety of new and improved polymers. In addition, catalyst compositions have also been used that comprise more than one catalyst or catalyst component, in effect, providing more than one active site to polymerize monomers during the polymerization process. Two or more different catalyst components have been used, for example, to produce multimodal polymers. However, there is continued focus in the industry on developing new and improved catalyst compositions. Some have focused on designing the catalyst compositions to produce new polymers, others on improved operability, and yet others on improving catalyst productivity.
Polymers produced with a multimodal molecular weight distribution offer unique product properties. Multimodal products can be produced by various methods, such as mixing different polymers, producing multimodal polymers under a series of reaction conditions, and reacting different catalysts under a single reactor condition. One method that has proven to be commercially viable is the production of multimodal catalyst systems wherein a catalyst system comprises more than one catalyst or catalyst component, thus, in effect, providing more than one active site to polymerize monomers during the polymerization process. When fed to a reaction system, each catalyst component concurrently produces a polymer component with distinct product properties. The net result is a polymer composition with distinct product advantages.
A number of different processes and techniques have been developed for making multimodal catalyst systems, and polymers with these multimodal catalyst systems. For example, bimodal catalyst compositions have been used that comprise a combination of a Group 15 containing metal compound (a bisamide compound) and a metallocene compound. One of the advantages of these multimodal catalyst systems lies in the molecular weight split (ratio of high to low molecular weight polymer produced). The productivity of a catalyst, that is, the amount of polymer produced per gram of the catalyst, as well as tailoring of the molecular weight split of polymer produced with these multimodal catalysts can be an important concern for polyolefin producers. Thus, there is a continued need for new and improved catalysts and catalyst compositions.